Extreme ultraviolet (EUV) light, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays) and including light at wavelengths at or about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates, e.g., silicon wafers.
Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has an element, e.g., xenon, lithium or tin, with an emission line in the EUV range. In one such method, often termed laser produced plasma (LPP) the required plasma can be produced by irradiating a target material, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam.
LPP and other high power laser applications often require a laser source meeting specific laser output requirements. These requirements may include power (or in the case of a pulsed laser—pulse energy and repetition rate), pulse duration, beam quality and wavelength. Generally, it is also desirable to optimize the initial laser cost, cost of laser operation, reliability and conversion efficiency (e.g., the ratio of EUV power output to electrical input). For example, and not by way of limitation, a particular LPP configuration, e.g., using tin targets, may operate efficiently using light at a wavelength of 10.6 μm, a pulse duration of 20-150 ns and a pulse energy of about 100 mJ.
With the above in mind, Applicants disclose systems and methods for efficiently producing laser light having the above described characteristics, together with teachings provided herein that are extendable to the design of laser sources to produce other specified laser output characteristics.